Chapter 4, page 2
Q & A about Quartz crystals
Q. I live in Mt Ida, Arkansas. I am interested in Geology and the differences in quartz crystal formations in shale and sandstone. Are surface pockets of crystal a good indication of what might be found deeper in the ground? I've talked to many crystal miners and their viewpoints are many and varied. Is there any right answer to locating pockets and veins of crystal? Stuart Schmitt, sos@ipa.net
A. Stuart, you have asked a series of complex questions. I will break them down and try to answer each one so all the readers can understand.
Part 1 - the differences in quartz veins and their crystal formation in shale versus sandstone host rock. Shale is composed of tiny particles of clay which have been compacted and squeezed and are bound together to form the rock we call shale. Sandstone is composed of sand grains with some type of cement or binder holding the grains together. This binder is often silica, or iron oxide, or clay. Fractures in shale expose only clay particles to any vein-forming hot water. Fractures in sandstone expose quartz grains and if the sandstone is silica cemented, then broken fresh faces of quartz to the incoming fluids.
This one fact is very important and explains why quartz crystal formation is different in these two rocks. The shale has few easy sites, compared to sandstone, for quartz to nucleate (that is, begin to grow). So in shale, quartz begins to be deposited uniformly over the entire surface. A lot of small milky crystal formation slowly begins, during growth, to produce larger oriented patches of larger milky crystal growth. Then growth is apparently rather rapid until the vein is completely filled. Usually shale-hosted veins have little collectable rock crystal (clear quartz) and usually what they do have is restricted to the middle of the veins.
Of course, in the Ouachita Mountains, these veins may have broken and reformed several times, making the system appear much more complex. Shale has another property due to its behavior when faulted or broken. It tends to smear along the break and seal itself off, effectively reducing the opportunity for silica-rich fluids to deposit quartz. Sandstones in the Ouachita Mountains were brittle and broke and fractured into many fragments during the mountain-building processes. When hot silica-rich waters reached the fractured sandstone beds, they had lots of channelways to move through. On the walls of these channelways were broken sand grains, often oriented properly to allow relatively rapid initial growth of crystal.
Rapid growth is often recognized by the presence of milky quartz. Some sand grains which were not oriented properly quickly dissolved and the available silica was redeposited on the growing crystal, along with silica which came into the vein with the hot water. When you look at a typical quartz cluster from Arkansas on sandstone matrix, the crystal is milky at the base where the crystal is attached to the matrix and clear at the tip. Now you know why. Rapid growth captures a lot of fluid and leaves behind many tiny holes which are filled with this fluid. Light refracts off this fluid and the sides of the tiny holes and the crystal appears milky.Part 2 - Are surface pockets an indication of what might be deeper in the ground? Most definitely! However, there are a few restrictions I will place on this answer. If you have pockets on the surface and the host rock does not change character, then your chances are good that crystal-bearing pockets extend to some depth. If the host rock was a sandstone at the surface and changed to a thick bed of shale, you are probably going to be out of luck on finding good veins in the shale. If the host rock is alternating thicker beds of sandstone and thin beds of shale and you find crystal pockets in the sandstone, you probably will have some crystal at depth.
Many local factors also enter into the situation. How close the site is to a major fault is important. Large low angle faults, geologists call thrust faults, may have shoved a large area of predominantly sandstone rock over underlying shale. The sandstone above the fault plane may be highly broken up and perfect for quartz deposition. But if the fluids never reached it for some reason, then even the properly "prepared" sandstone host will not have significant mineralization.
Before World War II, most of the local diggers in the Ouachita Mountains were convinced that if you were digging on a crystal bearing zone and the crystal veins became solid and milky at the bottom of where you were digging you would never get to any good clear crystal by digging any deeper. But the drilling and testing by the Federal Government during WW II proved them all wrong. Drilling showed clear, well-formed, crystal at 200 to 500 feet in depth at some of the abandoned locations. The Blocker Lead #4 site is an excellent example. This is now called the Ron Coleman mine and is near Blue Springs in Garland County.
You comment that the miner's opinions are many and varied concerning quartz bears discussion. Each miner's opinion is based on his/her own background, experience, and educational level. Even a college-educated person can have some unusual ideas if they are thinking about something which they have no formal education concerning. This is not to say that much of what the miners say is not based on something they have seen or experienced, but simply that a mineralogist or geologist, due to their formal training concerning things geological, might make the same observation as the miner and reach a totally different set of conclusions.
I am certain that if you tell some of the miners what I have stated here at least one of them will totally disagree with my thoughts and conclusions concerning quartz growth and formation. But he should be prepared to state, based on his own observations, what he thinks about crystal formation so that I might analyze his conclusions, too! If he can't or won't do that, then I can't take his comments seriously. The purpose of any discussion is not to show someone is right and the rest are wrong, but to come to an understanding of what people think, how they drew their conclusions, and which of those conclusions stand up best to critical analysis, thought and testing, so all can learn.Part 3 - Is there any right answer to locating pockets and veins of quartz crystal? Well, there are several things to do to make yourself more knowledgeable concerning how to find quartz veins with good clear crystal.
First, talk with all the people you can who are in the business. They have a lot of first-hand knowledge based on their experience that a novice miner needs to know. Many of the folks are down right friendly and will help you all they can. They might even let you assist them in mining some quartz so that you gain experience. Don't be bashful. Everyone starts to learn sometime. We are all on the same path. Some are just starting and others have been traveling on this journey for a while.
Second, you need to know something about general geology and the geology of the crystal-bearing areas. I think Garland County Community College in Hot Springs has a summer general geology course. Also, UALR has a summer course by one of the Earth Science Department instructors entitled "Geology of Arkansas". Take the GCCC course this summer and the Geology of Arkansas course next summer. Have some patience. It takes some time to learn and begin to understand how to apply what you have learned to what you want to do, which is to find some good quartz crystal.
I also suggest that, when you have time, you visit the library of the Arkansas Geological Commission in Little Rock. Tell the librarian that you wish to look at a copy of A. E. J. Engel's US Geological Survey Bulletin 973-E, Quartz Crystal Deposits of Western Arkansas. Also, pick up a free quartz pamphlet and a free copy of an article by Howard and Stone titled Quartz Crystal Deposits of Arkansas and Oklahoma.Good luck in your continuing education concerning this fascinating topic!
Q.Thank you for your comments concerning my answer to your previous question. Would you recommend following the veins deeper and what might we find?
A. Considering your statements about the unpredictability of where you find pockets, I would simply say that no two quartz veins are exactly alike. About the above question, yes I would dig deeper, at least until I reached the limits of whatever equipment I was working with.
One thing about digging crystal, you are not going to find anymore without further digging. This might be quite evident to you, but for my other readers, I must mention that during a mining operation and shortly after it ends is when the best specimens are recovered, simply because new excavations reveal areas that have not been reachable by surface collecting.
The average person working hard in one spot under good conditions can dig a hole 4'X4'X4' deep in mineralized ground with hand tools in a day. But a backhoe or trackhoe can dig that same hole in the same ground usually in less than 5 minutes! So power equipment is a must to locate any crystal pockets, then to keep the crystal from being damaged it is best dug by hand, if possible. As you well know, someone who doesn't know what they are doing with a trackhoe can damage a good pocket in seconds.
Q. My girlfriend and I have just recently started collecting some of the wonderful quartz crystals in the Hot Springs area, digging a little and buying some. We would like a little general information on the formation of clear quartz, how long it took for the crystals to form, temperatures, how long ago, some info on all the different shapes and names,Thank you very much, Park and Lisa
A. The age -- There is no isotopic method for directly dating the vein quartz, but several indirect approaches have been made. First, the veins are obviously younger than the rocks that contain them. In the Ouachita Mountains, the youngest sedimentary rocks present are Pennsylvanian in age. And quartz veins are present in all sedimentary units, but best developed in two Ordovician sandstones, the Blakely and the Crystal Mountain. Major veins are also present in some of the shale units, such as the Stanley (Mississippian). At one locality many years ago, adularia was discovered with the quartz. Adularia is a hydrothermal feldspar and can be dated. When dated, the adularia gave an age of Triassic, which is a little younger than what most geologists feel is a reasonable age for the quartz.
The most reasonable age appears to be late Pennsylvanian, some 286 million years ago for the last major deposition of the quartz. The veins formed in fractures in the uplifted Ouachita Mountains and late Pennsylvanian appears to be the last of that mountain building process. Some of the quartz is older and many veins show several periods of movement and rehealing. There are several igneous bodies in central Arkansas, and in the contact sedimentary rocks, we find alteration zones with smoky quartz. This quartz dates from about 100 million years ago (middle Cretaceous), the same age as the igneous rocks (they have been isotopically dated with some precision). No one can say how long the period of rock crystal quartz deposition lasted, but the cutoff date on the bulk of the crystal is Late Pennsylvanian. When it started, no one knows, but some vein formation could have begun by as early as late Ordovician.
No one knows how long it takes for a natural crystal to grow! It is dependent on how close the chemical and physical conditions approach those that would be ideal. Factors include composition of the silica-bearing fluids, temperature, pressure, Eh-Ph conditions, nucleation sites, and so forth. I can tell you that a small crystal has usually taken less time to form than a large one in the same pocket, but from pocket to pocket and from site to site, we just don't have the information to know. In the laboratory, under "ideal conditions", synthetic quartz crystals up to 1 pound or greater in weight are usually grown in about two weeks.
As to why some crystal is clear and some is not: Clear quartz crystal had a good life! No major breakage from earth movement and no stress or problems when it was growing. Very much Arkansas crystal has a milky matrix or base. The milky portion contains numerous fluid-filled cavities which scatter the light and present a whitish color. Many times "feathers" or planar flaws may be present. They represent breakage and rehealing of the crystal by additional silica deposition.
Sometimes you may even find a faulted (offset) and rehealed crystal. Many curved crystals are due to multiple breakage and rehealing events. Note I said curved. There is a type of quartz crystal that displays a twisting of the point, but I have never see one from Arkansas. Various colors of quartz are due to either elements like iron or manganese dispersed in the crystal chemically or due to natural irradiation of the crystal in the ground. Some mines have very clear crystal, tip to base, but these sites are the exception, not the rule. Normally, there has been enough structural adjustment of the ground (movement) during or immediately after crystal formation to create milky flaws in the quartz. When the vein is milky, then most of the crystal will have milky bases.
The temperature: This has been relatively well documented. The highest temperatures encountered are around 260 degrees C. Water boils at 100 degrees C unless confined. So the temperatures indicate a considerable depth of burial. You must have that for the water to reach such temperatures.
The mountains we see today are the products of millions of years of erosion. Many miners make a big deal about the fact that most veins are found on ridges or the sides of ridges. Well, it stands to reason. The most resistant layers of rock, sandstone, form the ridges. They were also, if fractured and broken up, the best sites for hot water to move through. Remember, the entire area we now see could have been under as much as 5 miles of rock! So the present day mountain forms have really nothing to do with the formation of quartz some 286 million years ago. With some experience of looking at quartz from various mines, you will find a difference in appearance from one mine to the next. Typical size, luster, clarity, length to width, matrix rock, et cetera that will aid you later if you see a piece, but the site is not given.
You could write the Arkansas Geological Commission and request some free literature on quartz. The address is given on this website under literature and info.Good luck and good diggin' Mike H.
Q. I was wondering what minerals and/or impurities cause quartz to become "phantomed"? I have found only one "phantomed" crystal--from Ron Coleman's Mine in Jessieville. This particular crystal's inclusions seem to appear gray. (I hope inclusion is the correct word to use here)
I have heard of other "phantoms" from the Mt. Ida area that have blue and/or green inclusions?! Do you know about these? Are there other interesting forms of quartz to be had from this general area? What about quartz scepters?
A. Phantoms are caused by a number of things that might happen while a crystal is growing. Any type of change, such as the chemistry of the water, growth interruption, or earth movement (structural adjustment) would have some effect on nearby quartz veins and the crystals forming in them. Sometimes just the type of host rock determines what type of inclusions may be present.
Now I should define the two terms I used, phantom and inclusion. A phantom is the form of the crystal expressed inside the present crystal faces. It may be due to fine-grained mineral matter that was deposited on the earlier and smaller crystal, or a fine coating of bubbles as the pocket periodically dried out, or as ground up rock dust created by nearby faulting that floated into the pocket and was deposited. An inclusion is simply any material encapsulated or enclosed by the mineral, in this case quartz, as the crystal grew. In gypsum, this may be sand or iron oxide.
In Arkansas quartz, inclusions can be many other minerals. Quartz has had a relatively lengthy time of growth, though episodic, when compared to other minerals. The following minerals and rock materials are often seen included in Arkansas quartz: adularia, thuringite (a variety of chlorite), cookeite, ankerite, calcite, pyrite-marcasite, quartz (as both sandstone grains and small crystals), brookite. Other minerals have been noted as inclusions, but are somewhat rarer in occurrence: cinnabar, stibnite, jamesonite, and galena.Phantoms take on several forms. Perhaps the most attractive are those crystals containing essentially complete caps or terminations coated with some material to make the point display well. Often these type consist of a fine coating of light-colored almost transparent mineral or tiny bubbles which formed on the point and were coated by the later deposition of clear quartz. Most often phantoms display only two or perhaps three of the prism or side faces of the crystal with a mineral or rock material coating them. Clouds of inclusions sometimes fill the early-formed crystal, which was then coated with colorless quartz.
One mine in Saline County was named the White Cloud mine due to the white cloudy phantoms that were often recovered from it. The materials most often composing the phantoms are: chlorite, bubbles, and tiny shale particles. All of the so-called blue phantoms, black phantoms, "manganese" phantoms and "manganese" inclusions and "carbon" phantoms are actually finely divided particles of black shale, a relatively common host rock in the Ouachita Mountains. I don't care what the crystal dealer or miner says, I have had many of these analyzed and the crystals are always aluminum-rich with no trace of manganese or carbon present. Even some earlier geologists were fouled up on this problem by making guesses instead of having the chemistry run on the material.
I should also say something about chlorite. Little work has been done on included chlorite in Arkansas crystal, but wherever chlorite is present, the host rock is shale-rich. The iron, silica, and other elements necessary to form chlorite in the quartz veins are evidently derived from leaching of the nearby shaley units.
Quartz scepters are rare in the deposits of the Ouachita Mountains. So are Japanese twinned quartz specimens. However, in the past few years, a notable number of Japanese twins have come from the Collier Creek mine and Fisher Mountain, both localities in Montgomery County, and even a few from the Old Coleman mine in Garland County.
Mike H.
Mr. Mikey,
Q. Why do quartz crystals have six sides? I found a quartz crystal with four sides, what does this mean? I also found a copperhead snake with 2 heads. Whats up with that? Thanks for answering my questions. When I grow up I want to be a geologist just like you. Your friend, Billy
B. Dear Billy, The structure and arrangement of the molecules that compose quartz (silicon and oxygen) combine in an orderly manner. This arrangement allows quartz crystal which forms in an open space to form as 6-sided crystals. Sometimes quartz may form either as misshapened crystals or be broken during formation and continue to form. Either way, the quartz may show some unusual forms, apparently 4 or even 3 sided, but believe me, with experience, you will be able to tell that something like this has happened.
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More answers to questions about quartz on the next page
Ch 4, page 2
mailto:jmichaelhoward@sbcglobal.net revised July 1998
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